I can't say this strongly enough: Consult an attorney.
Labor laws vary greatly from state to state. An 'employee manual' can, in some cases, help shield you from spurious claims. In other cases, it can become a real millstone.
Failing that, the only thing I would recommend as a 'short cut' would be to copy precisely the manual currently in use by some company that gets sued a lot. Or, the manual of a Union contractor. In either case, you can be sure that the manual has withstood extensive review and legal challenges.
Since you are in Illinois, I also suggest that you check out the "Illinois Institute for Continuing Legal Education" )or IICLE). They have a variety of excellent publications that cover nearly every legal topic. Don't let the prices scare you ... they're worth every dollar!
